Frank Lloyd Wright's Unity Temple, Oak Park, IL

Rewerts performed a comprehensive investigation into the condition of this historic, 1908 era concrete structure designed by Frank Lloyd Wright. This building is reportedly the first usage of reinforced concrete as both an architectural and structural material, in the United States, and is included on the National Register of Historic Places. Work involved investigating all aspects of the concrete structure of the building, including structural review of the cantilevered roof slabs, review of extensive cracking in the exterior concrete elements, review of carbonation-induced corrosion of reinforcing steel in both interior and exterior concrete elements of the building, review of pop-outs induced by expansion of slab and cinder aggregate particles in both interior and exterior concrete elements of the building, and review of freeze-thaw damage to exterior pavements.

The cantilevered concrete roof slabs were the focus of the investigation. The cantilevers exhibited an excessive (several inches) vertical deflection and concern had been raised regarding their stability and safety. Our analysis revealed this deflection was primarily due to long term creep of these lightweight, cinder aggregate concrete slabs.Our work involved preparation of very detailed plans and specifications for the repair of the cantilevered concrete roof slabs, and other areas of the building.

Cracking of one of the ornamental hollyhock columns on the north elevation presented unique challenges in terms of repair. We utilized a unique, first of a kind repair that involved leaving the delaminated concrete in place; injecting the crack with epoxy; followed by injecting a lithium based grout into the concrete in order to forestall further carbonation inducted corrosion of small reinforcing bars contained in the body of the column.Corrosion of reinforcing bars embedded behind the exposed aggregate finished concrete surface was a serious problem on the underside and outer edge of the cantilevered roof slabs, and at other areas on the exterior wall surfaces. This corrosion was determined to be due to carbonation of the near-surface regions of the concrete, and the underlying structural cinder concrete. Repair involved removal and replacement of the carbonated concrete on the underside of these cantilevered roof slabs. A very unique and one of a kind concrete removal system was employed, which involved use of expansive grout to non-percusively remove the concrete, without damaging the nearby art glass windows of the Church, or shattering the fragile cinder concrete in the roof slabs.

Work was performed while employed with Construction Technology Laboratories, Inc.

Thos. Rewerts & Co., LLC913-424-5180​t.rewerts@rewerts.com

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